(1) Field of the Invention
The present invention generally relates to a handwriting input apparatus, particularly, to a handwriting input apparatus, which is applied on a display panel of an electronic device.
(2) Description of the Prior Art
With the development of science and technology, input apparatus of electronic devices becomes pluralistic. Besides the familiar keyboard and mouse, a touch panel or a handwriting input apparatus becomes much more popular than before. Recently, the touch panels are applied on display panels of electronic devices such as ATM (automatic tell machine), bill payment machine and bill inquiring machine. Through the touch panel, an user can directly touch a icon, a word or a sentence, which is displayed on the display panel, to complete his/her input selection. The handwriting input apparatus, which is also applied on a display panel of a electronic device, provides higher detecting speed and detection sensitivity than the touch panel. Thus, the handwriting input apparatus is applied in more complicated electronic device such as panel computer or PDA.
Because the handwriting input apparatus is jointed with the display panel, it needs less space than other traditional input apparatus such as keyboard. This makes electronic products as PDA or panel computer meet their portable requirement. Another advantage of handwriting input apparatus is that it provides a more friendly human/machine interface than other input apparatus.
Please refer to FIG. 1. FIG. 1 shows a typical resistive touch panel 10. The touch panel 10 is applied in an electronic device. The touch panel 10 comprises a conductive sheet 12, an elastic conductive film 16 and a spacer 14. The spacer 14 are placed between the conductive sheet 12 and the elastic conductive film 16 to separate the conductive sheet 12 and the elastic conductive film 16. Two opposite sides 12a, 12b of the conductive sheet 12 connect to two different voltage levels. Thus a voltage gradient, which is perpendicular to a Y-axis shown in FIG. 1, is formed on the conductive sheet 12.
Two opposite sides 16a, 16b of the elastic conductive film 16 connect to two different voltage levels. Thus a voltage gradient, which is perpendicular to a X-axis shown in FIG. 1, is formed on the elastic conductive film 16. While an user's finger exerts pressure on the elastic conductive film 16 to make the elastic conductive film 16 touch the conductive sheet 12. The distribution situations of the voltage levels on the conductive sheet 12 and the elastic conductive film 16 are changed. By measuring the changed voltage levels, a touched position of the finger is able to be detected. The drawbacks of the resistive touch panel 10 is the poor detecting speed that cannot meet the requirement of handwriting input.
Please refer to FIG. 2A and FIG. 2B. FIG. 2A is a top view of a handwriting panel 20. FIG. 2B is a cross section view along line a-a of the touch panel 20 shown in FIG. 2A. The handwriting panel 20 comprises a thin-film transistors substrate 21, a plurality of conductive islet 27, an elastic conductive film 28 and a spacer 29.
As shown in FIG. 2A and FIG. 2B, the thin-film transistors substrate 21 comprises a substrate 25, a plurality of thin-film transistors 22 arranged as an array, a plurality of data lines 24, a plurality of scan lines 26, and a passivation layer 23. The plurality of data lines 24 disposed on the substrate 25 are arranged in a column direction; and the plurality of scan lines 26, which are also disposed on the substrate 25, are arranged in a row direction. The substrate 25 is divided into several compartments by the data lines 24 and the scan lines 26. Each of the thin-film transistor 22 is located in each compartment respectively. The drain of the thin-film transistor 22 electrically connects to the data line 24. The gate of the thin-film transistor 22 electrically connects to the scan line 24. The passivation layer 23 is disposed on the substrate 25 for protecting the plurality of thin-film transistors 21, the plurality of scan lines 26 and the plurality of data lines 24.
A plurality of conductive islets 27 are formed on the surface of the thin-film transistors substrate 21. Each of the conductive islets 27 electrically connects to the source of one thin-film transistor 22 through a through hole within the passivation layer 23. The spacer 29 is needed for separating the plurality of conductive islets 27 with the elastic conductive film 28. As shown in FIG. 2B, the spacer 29 is disposed on the thin-film transistors substrate 21; and it is located on the margin area of the thin-film transistors substrate 21 as shown in FIG. 2A.
While an user exerts pressure on the handwriting panel 20, with a finger or a touch pen, to make a portion of the elastic conductive film 28 touch with one or several conductive islets 27, at least one electrical signal is produced through the conduction of the elastic conductive film 28 and the corresponding touched conductive islet 27. The produced electrical signal is transferred to the source of the thin-film transistor 27. The produced electrical signal is scanned through each data line 24 sequentially by switching the gates, which are operated by the plurality of scan lines 26. By these, the touched position is detected by the produced electrical signal.
The scan and detecting speed of the handwriting panel 20 is fast enough for handwriting input. For example, under a scan frequency of 60 Hz, it only takes 16 milliseconds to complete a scan over the whole handwriting panel 20. Utilizing the integrated circuit and semiconductor producing technology, a thin-film transistors substrate 21 with high integration density is available. Thus, the handwriting panel 20 is able to meet the requirement of handwriting input.
However, the thin-film transistors substrate 21 within the handwriting panel 20 is very similar to one of the substrates of the LCD (liquid crystal display) panel, which comprises a plurality of thin-film transistors and relatively costs much. Besides the disadvantage of relatively high cost, the handwriting panel 20 also has a drawback of poor transmittance. This drawback counts in the situation that the handwriting panel 20 is applied on a display panel. Take the LCD panel for instance, if the handwriting panel 20 is disposed on the LCD panel, the light from a backlight source has to transmitted through a bottom substrate of LCD, which is very similar to the thin-film transistors substrate 21, a upper substrate of LCD, which is usually a color filter glass, and the handwriting panel 20 so as to reach the user's eye. Therefore, the handwriting panel 20, which has a complicated structure, might reduce the brightness of the display panel and disadvantage the image uniformity.
Another drawback of the prior handwriting panel 20 is the supporting ability. The elastic conductive film 28 is supported by the spacer 29. But the spacer 29 is generally disposed only on the margin area of the thin-film transistors substrate 21. Hence, the major portion of the elastic conductive film 28 is unsupported. Besides, the elastic conductive film 28 is usually made from elastic materials such as PET, PMMA, PC or PE, which are not easy to control its flatness while manufacturing.
Furthermore, after repeatedly use, the material intensity of the elastic conductive film 28 would decrease, or the material would become tired. While the tired elastic conductive film 28 is not able to be separated from the below conductive islet 27, the handwriting panel 20 will totally lost its function. The same drawback also appears in the touch panel 10 illustrated with FIG. 1.
As described above, while the handwriting input apparatus become important in many kinds of electrical device for obtaining a more friendly human/machine interface and for space-saving for the electrical device, the technique how to develop a handwriting input apparatus without the previously described disadvantages is now an important issue in the art.